Media Type Specifications and
Registration Procedures
Oracle800 Royal OaksMonroviaCA91016-6347USAned+ietf@mrochek.com1770 Massachusetts Ave, #322CambridgeMA02140USAjohn+ietf@jck.comAT&T Laboratories200 Laurel Ave.MiddletownNJ07748USAtony+mtsuffix@maillennium.att.comApplications
RFCRequest for CommentsMIMEmedia typesI-DInternet-Draft
This document defines procedures for the specification and
registration of media types for use in HTTP, MIME and other Internet
protocols.
Recent Internet protocols have been carefully designed to be easily extensible
in certain areas. In particular, many protocols, including but not limited
to HTTP and MIME,
are capable of carrying arbitrary labeled content.
The mechanism used to label such content is a media type, consisting of a
top-level type and a subtype, which is further structured into trees.
Optionally, media types can define companion data, known as parameters.
A registration process is needed for these labels, so that that the set of
such values are defined in a reasonably orderly, well-specified, and public
manner.
This document specifies the criteria for media type registrations and
defines the procedures to be used to register media types
() as well as media type structured suffixes
() in the Internet Assigned Numbers
Authority (IANA) central registry.
The location of the media type registry managed by these procedures is:
http://www.iana.org/assignments/media-types/
The media type registration process was initially defined for registering
media types for use in the context of the asynchronous Internet
mail environment. In this mail environment there is a need to limit the number
of possible media types, to increase the likelihood of interoperability when the
capabilities of the remote mail system are not known. As media types are used
in new environments in which the proliferation of media types is not a hindrance
to interoperability, the original procedure proved excessively restrictive and had
to be generalized. This was initially done in , but
the procedure defined there was still part of the MIME document set. The
media type specification and registration procedure is now a
separate document, to make it clear that it is independent of MIME.
It may be desirable to restrict the use of media types to specific environments
or to prohibit their use in other environments. This specification incorporates such
restrictions into media type registrations in a systematic way.
See for additional discussion.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in
when they appear in ALL CAPS. They may also appear in lower or mixed case as
plain English words, without any normative meaning.
This specification makes use of the Augmented
Backus-Naur Form (ABNF) notation, including the core rules defined in
Appendix A of that document.
Registration of a new media type or types starts with the construction of a
registration proposal. Registration may occur within several different
registration trees that have different requirements, as discussed below. In
general, a new registration proposal is circulated and reviewed in a fashion
appropriate to the tree involved. The media type is then registered if the
proposal is acceptable. The following sections describe the requirements and
procedures used for each of the different registration trees.
In order to increase the efficiency and flexibility of the registration
process, different structures of subtype names can be registered to accommodate
the different natural requirements for, e.g., a subtype that will be
recommended for wide support and implementation by the Internet community, or a
subtype that is used to move files associated with proprietary software. The
following subsections define registration "trees" that are distinguished by the
use of faceted names, e.g., subtype names that begin with a a "tree." prefix.
Note that some media types defined prior to this document do not conform to the
naming conventions described below. See Appendix A for a discussion of them.
The standards tree is intended for types of general interest to the
Internet community. Registrations in the standards tree MUST be either:
in the case of registrations in IETF specifications, approved directly by the
IESG, or
registered by a recognized standards body using the "Specification Required"
IANA registration policy (which implies Expert Review).
The first procedure is used for registering registrations from IETF
Consensus documents, or in rare cases when registering a grandfathered (see
) and/or otherwise incomplete
registration is in the interest of the Internet community. The registration
proposal MUST be published as an RFC. When the RFC is in the IETF
stream it is an IETF Consensus RFC, which can be on the Standards
Track, a BCP, Informational, or Experimental. Registrations
published in non-IETF RFC streams are also allowed, and require IESG
approval. A registration can be either in a standalone
"registration only" RFC or incorporated into a more general
specification of some sort.
In the second case the IESG makes a one time decision on whether the
registration submitter represents a recognized standards body; after
that, a Media Types Reviewer (Designated Expert or a group of
Designated Experts) performs the Expert Review as specified in this
document. Subsequent submissions from the same source do not involve
the IESG. The format MUST be described by a formal standards
specification produced by the submitting standards body.
Media types in the standards tree MUST NOT have faceted names, unless
they are grandfathered in using the process described in
.
The "owner" of a media type registered in the standards tree is
assumed to be the standards body itself. Modification or alteration
of the specification uses the same level of processing (e.g.,
a registration submitted on Standards Track can be revised in another
Standards Track RFC, but cannot be revised in an Informational RFC)
required for the initial registration.
Standards-tree registrations from recognized standards bodies are
submitted directly to the IANA, where they will undergo Expert Review
prior to approval. In this case, the Expert
Reviewer(s) will, among other things, ensure that the required specification
provides adequate documentation.
The vendor tree is used for media types associated with publicly available
products. "Vendor" and "producer" are construed very broadly in this context
and are considered equivalent. Note that industry consortia as
well as non-commercial entities that do not qualify as recognized standards
bodies can quite appropriately register media types in the vendor tree.
A registration may be placed in the vendor tree by anyone who needs to
interchange files associated with some product or set of products. However,
the registration properly belongs to the vendor or organization producing the
software that employs the type being registered, and that vendor or organization
can at any time elect to assert ownership of a registration done by a third party
in order to correct or update it. See
for additional information.
When a third party registers a type on behalf of someone else both entities
SHOULD be noted in the Change Controller field in the registration.
One possible format for this would be "Foo, on behalf of Bar".
Registrations in the vendor tree will be distinguished by the leading facet
"vnd.". That may be followed, at the discretion of the registrant, by either
a media subtype name from a well-known producer (e.g., "vnd.mudpie") or by an
IANA-approved designation of the producer's name that is followed by a
media type or product designation (e.g., vnd.bigcompany.funnypictures).
While public exposure and review of media types to be registered in the vendor
tree is not required, using the media-types@iana.org mailing list for review is
encouraged to improve the quality of those specifications. Registrations
in the vendor tree may be submitted directly to the IANA, where they will
undergo Expert Review prior to approval.
Registrations for media types created experimentally or as part of products
that are not distributed commercially may be registered in the personal or
vanity tree. The registrations are distinguished by the leading facet "prs.".
The owner of "personal" registrations and associated specifications is the
person or entity making the registration, or one to whom responsibility has
been transferred as described below.
While public exposure and review of media types to be registered in the
personal tree is not required, using the media-types@iana.org mailing list
(see ) for review is encouraged to improve the
quality of those specifications. Registrations in the personal tree may be
submitted directly to the IANA, where they will undergo Expert Review
prior to approval.
Subtype names with "x." as the first facet may be used for types intended
exclusively for use in private, local environments. Types in this tree
cannot be registered and are intended for use only with the active agreement
of the parties exchanging them.
However, with the simplified registration procedures described above for vendor
and personal trees, it should rarely, if ever, be necessary to use unregistered
types. Therefore, use of types in the "x." tree is strongly discouraged.
Note that types with names beginning with "x-" are no longer considered to be
members of this tree (see ). Also note
that if a generally useful and widely deployed type incorrectly ends up with
an "x-" name prefix, it MAY be registered using its current name in an
alternate tree by following the procedure defined in
.
From time to time and as required by the community, new top-level registration
trees may be created by IETF Standards Action. It is explicitly assumed that
these trees may be created for external registration and management by
well-known permanent bodies; for example, scientific societies may register
media types specific to the sciences they cover. In general, the quality of
review of specifications for one of these additional registration trees is
expected to be equivalent to registrations in the standards tree
by a recognized Standards Development Organization. When the IETF
performs such review, it needs to consider the greater expertise
of the requesting body with respect to the subject media type.
Media type registrations are all expected to conform to various
requirements laid out in the following sections. Note that requirement
specifics sometimes vary depending on the registration tree, again as detailed
in the following sections.
Media types MUST function as actual media formats. Registration of things
that are better thought of as a transfer encoding, as a charset, or as a
collection of separate entities of another type, is not allowed. For example,
although applications exist to decode the base64 transfer encoding
, base64 cannot be registered as a media type.
This requirement applies regardless of the registration tree involved.
All registered media types MUST be assigned top-level type and subtype names.
The combination of these names serves to uniquely identify the media type,
and the subtype name facet (or the absence of one) identifies the registration
tree. Both top-level type and subtype names are case-insensitive.
Type and subtype names MUST conform to the following ABNF:
Note that this syntax is somewhat more restrictive than what is allowed by
the ABNF in section 5.1 of or section 4.2 of
. Also note that while this syntax allows names of up
to 127 characters, implementation limits may make such long names problematic.
For this reason the components of names SHOULD be limited to 64 characters.
Although the name syntax treats "." as equivalent to any other character,
characters before any initial "." always specify the registration facet.
Note that this means that facet-less standards tree registrations cannot use
periods in the subtype name.
Similarly, "+" is used in subtype names to introduce a structured syntax
specifier suffix. Structured syntax suffix requirements are specified in
.
While it is possible for a given media type to be assigned additional names,
the use of different names to identify the same media type is discouraged.
These requirements apply regardless of the registration tree involved.
The choice of top-level type MUST take into account the nature of media
type involved. New subtypes of top-level types MUST conform to the restrictions
of the top-level type, if any. The following sections describe each of the
initial set of top-level types and their associated restrictions. Additionally,
various protocols, including but not limited to HTTP and MIME, MAY impose
additional restrictions on the media types they can transport. (See
for additional information on the restrictions
MIME imposes.)
The "text" top-level type is intended for sending material that is principally
textual in form.
Many subtypes of text, notably including the subtype "text/plain", which is a
generic subtype for plain text defined in ,
define a "charset" parameter. If a "charset" parameter is defined for a
particular subtype of text, it MUST be used to specify a charset name
defined in accordance to the procedures laid out in .
As specified in ,
a "charset" parameter SHOULD NOT be specified when charset information is
transported inside the payload (e.g., as in "text/xml").
If a "charset" parameter is specified, it SHOULD be a required parameter,
eliminating the options of specifying a default value. If there is a strong reason
for the parameter to be optional despite this advice, each subtype MAY specify
its own default value, or alternately, it MAY specify that there is no default
value. Finally, the "UTF-8" charset SHOULD be selected
as the default. See
for additional information on the use of "charset" parameters in conjunction
with subtypes of text.
Regardless of what approach is chosen, all new text/* registrations
MUST clearly specify how the charset is determined; relying on the US-ASCII
default defined in Section 4.1.2 of is no longer
permitted. If explanatory text is needed this SHOULD be placed in the
additional information section of the registration.
Plain text does not provide for or allow formatting commands, font attribute
specifications, processing instructions, interpretation directives, or content
markup. Plain text is seen simply as a linear sequence of characters, possibly
interrupted by line breaks or page breaks. Plain text MAY allow the stacking of
several characters in the same position in the text. Plain text in scripts
like Arabic and Hebrew may also include facilities that allow the arbitrary
mixing of text segments with different writing directions.
Beyond plain text, there are many formats for representing what might be known
as "rich text". An interesting characteristic of many such representations is
that they are to some extent readable even without the software that interprets
them. It is useful to distinguish them, at the highest level, from such
unreadable data as images, audio, or text represented in an unreadable form.
In the absence of appropriate interpretation software, it is reasonable to present
subtypes of "text" to the user, while it is not reasonable to do so with most
non-textual data. Such formatted textual data can be represented using
subtypes of "text".
A top-level type of "image" indicates that the content specifies one or more
individual images. The subtype names the specific image format.
A top-level type of "audio" indicates that the content contains audio data.
The subtype names the specific audio format.
A top-level type of "video" indicates that the content specifies a time-varying-picture
image, possibly with color and coordinated sound. The term 'video' is used in
its most generic sense, rather than with reference to any particular technology
or format, and is not meant to preclude subtypes such as animated drawings
encoded compactly.
Note that although in general the mixing of multiple kinds media in a single
body is discouraged , it is recognized that many
video formats include a representation for synchronized audio and/or text, and
this is explicitly permitted for subtypes of "video".
The "application" top-level type is to be used for discrete data that do not
fit under any of the other type names, and particularly for data to be processed
by some type of application program. This is information that must be
processed by an application before it is viewable or usable by a user.
Expected uses for the "application" type name include but are not limited
to file transfer,
spreadsheets, presentations, scheduling data, and languages for
"active" (computational) material. (The last, in particular, can pose
security problems that must be understood by implementors. The
"application/postscript" media type registration in
provides a good example of how to handle these issues.)
For example, a meeting scheduler might define a standard representation for
information about proposed meeting dates. An intelligent user agent would use
this information to conduct a dialog with the user, and might then send
additional material based on that dialog. More generally, there have been
several "active" languages developed in which programs in a suitably
specialized language are transported to a remote location and automatically run
in the recipient's environment.
Such applications may be defined as subtypes of the "application" top-level type.
The subtype of "application" will often either be the name or include part of
the name of the application for which the data are intended. This does not
mean, however, that any application program name may simply be used freely as a
subtype of "application"; the subtype needs to be registered.
Multipart and message are composite types, that is, they provide a means
of encapsulating zero or more objects, each one a separate media type.
All subtypes of multipart and message MUST conform to the syntax rules
and other requirements specified in and amended
by Section 3.5 of .
In some cases a new media type may not "fit" under any currently defined
top-level type names. Such cases are expected to be quite rare. However, if
such a case does arise a new type name can be defined to accommodate it. Such
a definition MUST be done via standards-track RFC; no other mechanism can be
used to define additional type names.
XML in MIME defined the first such augmentation to the
media type definition to additionally specify the underlying structure
of that media type. To quote:
This document also standardizes a convention (using
the suffix '+xml') for naming media types ... when those
media types represent XML MIME (Multipurpose
Internet Mail Extensions) entities.
That is, it specified a suffix (in that case, "+xml") to be
appended to the base subtype name.
Since this was published, the de facto practice has arisen for using this
suffix convention for other well-known structuring syntaxes.
In particular, media types have been registered with suffixes
such as "+der", "+fastinfoset" and "+json". This specification formalizes this
practice and sets up a registry for structured type name suffixes.
The primary guideline for whether a structured type name suffix is
registrable is that it be described by a readily-available description, preferably
within a document published by an established standards organization, and for
which there's a reference that can be used in a Normative References section of
an RFC.
Media types that make use of a named structured syntax SHOULD
use the appropriate registered "+suffix" for that structured syntax
when they are registered. By the same token, media types MUST NOT be given
names incorporating suffixes for structured syntaxes they do not actually
employ. "+suffix" constructs for as-yet unregistered structured syntaxes
SHOULD NOT be used, given the possibility of conflicts with future
suffix definitions.
In some cases a single media type may have been widely deployed prior to
registration under multiple names. In such cases a preferred name MUST be
chosen for the media type and applications MUST use this to be compliant
with the type's registration. However, a list of deprecated aliases the
type is known by MAY be supplied as additional information in order to
assist applications in processing the media type properly.
Media types MAY elect to use one or more media type parameters, or some
parameters may be automatically made available to the media type by virtue of
being a subtype of a content type that defines a set of parameters applicable
to any of its subtypes. In either case, the names, values, and meanings of any
parameters MUST be fully specified when a media type is registered in the standards
tree, and SHOULD be specified as completely as possible when media types are
registered in the vendor or personal trees.
Parameter names have the syntax as media type names and values:
Note that this syntax is somewhat more restrictive than what is allowed by the ABNF
in and amended by .
Parameter names are case-insensitive and no meaning is attached to the
order in which they appear. It is an error for a specific parameter to be
specified more than once.
There is no defined syntax for parameter values. Therefore registrations MUST
specify parameter value syntax. Additionally, some transports impose restrictions
on parameter value syntax, so care needs be taken to limit the use of potentially
problematic syntaxes; e.g., pure binary valued parameters, while permitted in some
protocols, are best avoided.
Note that a protocol can impose further restrictions on parameter value
syntax, depending on how it chooses to represent parameters. Both MIME
and HTTP
allow binary parameters as
well as parameter values expressed in a specific charset, but other
protocols may be less flexible.
New parameters SHOULD NOT be defined as a way to introduce new functionality in
types registered in the standards tree, although new parameters MAY be added to
convey additional information that does not otherwise change existing
functionality. An example of this would be a "revision" parameter to indicate
a revision level of an external specification such as JPEG. Similar
behavior is encouraged for media types registered in the vendor
or personal trees, but is not required.
Changes to parameters (including the introduction of new ones) is
managed in the same manner as other changes to the media type; see
.
All registered media types MUST employ a single, canonical data format,
regardless of registration tree.
A permanent and readily available public specification of the format for the
media type MUST exist for all types registered in the standards tree, and this
specification MUST provide sufficient detail so that interoperability between
independent implementations using the media type is possible. This specification
MUST at a minimum be referenced by, if it is not actually included in, the
media type registration proposal itself.
The specifications of format and processing particulars may or may not be
publicly available for media types registered in the vendor and personal trees,
and such registrations are explicitly permitted to limit the information in the
registration to which software and version produce or process such media types.
As such, references to or inclusion of format specifications in registrations is
encouraged but not required. Note, however, that the
public availability of a meaningful specification will
often make the difference between simply having a name
reserved so that there are no conflicts with other uses
and having the potential for other implementations of
the media type and useful interoperation with them.
Some media types involve the use of patented technology. The registration of
media types involving patented technology is specifically permitted. However,
the restrictions set forth in BCP 79 and
BCP 78 on the use of patented technology in IETF
standards-track protocols must be respected when the specification of a
media type is part of a standards-track protocol. In addition, other standards
bodies making use of the standards tree may have their own rules regarding
intellectual property that must be observed in their registrations.
IPR disclosures for registrations in the vendor and personal tree are encouraged
but not required.
Ideally media types will be defined so they interoperate across as many systems and
applications as possible. However, some media types will inevitably have
problems interoperating across different platforms. Problems with different
versions, byte ordering, and specifics of gateway handling can and will arise.
Universal interoperability of media types is not required, but known
interoperability issues SHOULD be identified whenever possible. Publication of
a media type does not require an exhaustive review of interoperability, and
the interoperability considerations section is subject to continuing
evaluation.
These recommendations in this subsection apply regardless of the registration
tree involved.
An analysis of security issues MUST be done for all types registered
in the standards tree. A similar analysis for media types registered in the
vendor or personal trees is encouraged but not required. However, regardless
of what security analysis has or has not been done, all descriptions of
security issues MUST be as accurate as possible regardless of registration
tree. In particular, the security considerations MUST NOT state that there are
"no security issues associated with this type". Security considerations for
types in the vendor or personal tree MAY say that "the security issues
associates with this type have not been assessed".
There is absolutely no requirement that media types registered in any tree be
secure or completely free from risks. Nevertheless, all known security risks
MUST be identified in the registration of a media type, again regardless of
registration tree.
The security considerations section of all registrations is subject to
continuing evaluation and modification, and in particular MAY be extended by
use of the "comments on media types" mechanism described in
below.
Some of the issues that need to be examined and described in a security analysis
of a media type are:
Complex media types may include provisions for directives that institute
actions on a recipient's files or other resources. In many cases provision is
made for originators to specify arbitrary actions in an unrestricted fashion
that may then have devastating effects. See the registration of the
application/postscript media type in
for an example of such directives and how they can be described in a media
type registration.
Any security analysis MUST state whether or not they employ such "active
content", and if they do, they MUST state what steps have been taken,
or MUST be taken by applications of the media type, to protect
users of the media type from harm.
Complex media types may include provisions for directives that institute
actions that, while not directly harmful to the recipient, may result in
disclosure of information that either facilitates a subsequent attack or else
violates a recipient's privacy in some way. Again, the registration of the
application/postscript media type illustrates how such directives can be
handled.
A media type that employs compression may provide an opportunity for
sending a small amount of data that, when received and evaluated, expands
enormously to consume all of the recipient's resources. All media types
SHOULD state whether or not they employ compression, and if they do they
SHOULD discuss what steps need to be taken to avoid such attacks.
A media type might be targeted for applications that require some sort of
security assurance but not provide the necessary security mechanisms
themselves. For example, a media type could be defined for storage of
sensitive medical information that in turn requires external
confidentiality and integrity protection services, or which is designed for
use only within a secure environment. Types SHOULD always document whether
or not they need such services in their security considerations.
There are a number of additional requirements specific to the registration of
XML media types. These requirements are specified in .
Some transports impose restrictions on the type of data they can carry. For
example, Internet mail traditionally was limited to 7bit US-ASCII text.
Encoding schemes are often used to work around such transport limitations.
It is therefore useful to note what sort of data a media type can consist of
as part of its registration. An "encoding considerations" field is provided for
this purpose. Possible values of this field are:
The content of the media type consists solely of CRLF-delimited 7bit US-ASCII
text.
The content of the media type consists solely of CRLF-delimited 8bit text.
The content consists of an unrestricted sequence of octets.
The content consists of a series of frames or packets without internal framing
or alignment indicators. Additional out-of-band information is needed to
interpret the data properly, including but not necessarily limited to,
knowledge of the boundaries between successive frames
and knowledge of the transport mechanism. Note that media types
of this sort cannot simply be stored in a file or transported as a simple
stream of octets; therefore, such media types are unsuitable for use
in many traditional protocols. A commonly used transport with framed encoding
is the Real-time Transport Protocol, RTP. Additional rules for framed encodings
defined for transport using RTP are given in .
Additional restrictions on 7bit and 8bit text are given in Section 4.1.1 of
.
In the asynchronous mail environment, where information on the capabilities of
the remote mail agent is frequently not available to the sender, maximum
interoperability is attained by restricting the media types used to
those "common" formats expected to be widely implemented. This was asserted in
the past as a reason to limit the number of possible media types, and resulted
in a registration process with a significant hurdle and delay for those
registering media types.
However, the need for "common" media types does not require limiting the
registration of new media types. If a limited set of media types is recommended
for a particular application, that should be asserted by a separate
applicability statement specific for the application and/or environment.
Therefore, universal support and implementation of a media type is NOT a
requirement for registration. However, if a media type is explicitly intended
for limited use, this MUST be noted in its registration. The "Restrictions on
Usage" field is provided for this purpose.
Media types registered in the standards tree by the IETF itself MUST be
published as RFCs. RFC publication of vendor and personal media type
registrations is allowed but not required. In all cases the IANA will retain
copies of all media type registrations and "publish" them as part of the media
types registration tree itself.
As stated previously, standards tree registrations for media types defined in
documents produced by other standards bodies MUST be described by a formal
standards specification produced by that body. Additionally, any
copyright on the registration template MUST allow the IANA to copy it into
the IANA registry.
Other than IETF registrations in the standards tree, the registration of a media
type does not imply endorsement, approval, or recommendation by the IANA or the
IETF or even certification that the specification is adequate. To become an
Internet Standard, a protocol or data object must go through the IETF standards
process. While it provides additional assurances when it is appropriate, this
is too difficult and too lengthy a process for the convenient registration of
media types.
The standards tree exists for media types that do require a substantive
review and approval process in a recognized standards body.
The vendor and personal trees exist for those media types
that do not require such a process. It is expected that applicability statements
for particular applications will be published from time to time in the IETF,
recommending implementation of, and support for, media types that have proven
particularly useful in those contexts.
As discussed above, registration of a top-level type requires
Standards Action in the IETF and, hence, the publication of a RFC on
the Standards Track.
Media type registrations can specify how applications should interpret
fragment identifiers (specified in section 3.5 of )
associated with the media type.
Media types are encouraged to adopt fragment identifier schemes that are used
with semantically similar media types. In particular, media types that use a
named structured syntax with a registered "+suffix" MUST follow whatever
fragment identifier rules are given in the structured syntax suffix
registration.
Various sorts of optional information SHOULD be included in the specification
of a media type if it is available:
Magic number(s) (length, octet values). Magic numbers are byte sequences that
are always present at a given place in the file and thus can be used to identify
entities as being of a given media type.
File name extension(s) commonly used on one or more platforms to indicate that
some file contains a given media type.
Mac OS File Type code(s) (4 octets) used to label files containing a given
media type. Some discussion of Macintosh file type codes and their purpose can
be found in .
In the case of a registration in the standards tree, this additional information
MAY be provided in the formal specification of the media type format. It is suggested
that this be done by incorporating the IANA media type registration form into the
format specification itself.
The media type registration procedure is not a formal
standards process, but rather an administrative procedure
intended to allow community comment and sanity checking
without excessive time delay.
Normal IETF processes need to be followed for all IETF
registrations in the standards tree. The posting of an
Internet Draft is a necessary first step, followed by
posting to the media-types@iana.org list as discussed below.
Notice of a potential media type registration in the standards tree SHOULD be
sent to the media-types@iana.org mailing list for review. This mailing list
has been established for the purpose of reviewing proposed media and access
types. Registrations in other trees MAY be sent to the list for review as well;
doing so is entirely OPTIONAL, but is strongly encouraged.
The intent of the public posting to this list is to solicit comments and
feedback on the choice of type/subtype name, the unambiguity of the references
with respect to versions and external profiling information, and a review of any
interoperability or security considerations. The submitter may submit a revised
registration proposal or abandon the registration completely and at any time.
Media types registered in the standards tree by the IETF itself MUST be
reviewed and approved by the IESG as part of the normal standards process.
Standards tree registrations by recognized standards bodies as well as
registrations in the vendor and personal tree are submitted directly
to the IANA, unless other arrangements were made as part of a liaison
agreement. In either case posting the registration to the media-types@iana.org
list for review prior to submission is strongly encouraged.
Registration requests can be sent to
iana@iana.org. A web form for registration requests is also available:
http://www.iana.org/cgi-bin/mediatypes.pl
Standardization processes often take considerable time to complete. In order
to facilitate prototyping and testing it is often helpful to assign identifiers,
including but not limited to media types, early in the process. This way
identifiers used during standards development can remain unchanged once the
process is complete and implementations and documentation do not have to be
updated.
Accordingly, a provisional registration process is provided to support early
assignment of media type names in the standards tree. A provisional registration
MAY be submitted to IANA for standards tree types. The only required fields in
such registrations are the media type name and contact information (including
the standards body name).
Upon receipt of a provisional registration, IANA will check the name and
contact information, then publish the registration in a separate publicly
visible provisional registration list.
Provisional registrations MAY be updated or abandoned at any time.
When the registration is abandoned the media type is no longer registered in
any sense; it can subsequently be registered just like any other unassigned
media type name.
With the exception of provisional standards tree registrations,
registrations submitted to the IANA will be passed on to the media types
reviewer. The media types reviewer, who is appointed by the IETF Applications
Area Director(s), will review the registration to make sure it meets the
requirements set forth in this document. Registrations that do not meet
these requirements will be returned to the submitter for revision.
Decisions made by the media types reviewer may be appealed to the IESG using
the procedure specified in section 6.5.4 of .
Once a media type registration has passed review, the IANA will register the
media type and make the media type registration available to the community.
In the case of standards tree registrations from other standards bodies IANA
will also check that the submitter is in fact a recognized standards body. If
the submitter is not currently recognized as such the IESG will be asked to
confirm their status. Recognition from the IESG MUST be obtained before a
standards tree registration can proceed.
Comments on registered media types may be submitted by members of the
community to the IANA at iana@iana.org. These comments will be reviewed by the
media types reviewer and then passed on to the "owner" of the media type if possible.
Submitters of comments may request that their comment be attached to the
media type registration itself, and if the IANA, in consultation with the
media types reviewer, approves, the comment
will be made accessible in conjunction with the type registration.
Once a media type has been published by the IANA, the owner may request a change
to its definition. The descriptions of the different registration trees above
designate the "owners" of each type of registration.
The same procedure that would be appropriate for the original registration
request is used to process a change request.
Media type registrations may not be deleted; media types that are no
longer believed appropriate for use can be declared OBSOLETE by a
change to their "intended use" field; such media types will be clearly
marked in the lists published by the IANA.
Significant changes to a media type's definition should be requested only when
there are serious omissions or errors in
the published specification. When review is required, a change request may be
denied if it renders entities that were valid under the previous definition
invalid under the new definition.
The owner of a media type may pass responsibility to another person or agency
by informing the IANA; this can be done without discussion or review.
The IESG may reassign responsibility for a media type. The most common case of
this will be to enable changes to be made to types where the author of the
registration has died, moved out of contact or is otherwise unable to make
changes that are important to the community.
Type name:
Subtype name:
Required parameters:
Optional parameters:
Encoding considerations:
Security considerations:
Interoperability considerations:
Published specification:
Applications that use this media type:
Fragment identifier considerations:
Additional information:
Deprecated alias names for this type:
Magic number(s):
File extension(s):
Macintosh file type code(s):
Person & email address to contact for further information:
Intended usage:
(One of COMMON, LIMITED USE or OBSOLETE.)
Restrictions on usage:
(Any restrictions on where the media type can be used go here.)
Author:
Change controller:
Provisional registration? (standards tree only):
(Any other information that the author deems interesting may be
added below this line.)
"N/A", written exactly that way, can be used in any field if desired to
emphasize the fact that it does not apply or that the question
was not omitted by accident. Do not use 'none' or other words
that could be mistaken for a response.
Limited use media types should also note in the applications list whether or not
that list is exhaustive.
Someone wishing to define a "+suffix" name for a structured syntax for use with
a new media type registration SHOULD:
Check IANA's registry of media type name suffixes to see whether
or not there is already an entry for that well-defined structured syntax.
If there is no entry for their suffix scheme, fill out the template
(specified in )
and include that with the media type registration.
The template may be contained in an Internet Draft, alone or as part of
some other protocol specification. The template may also be submitted
in some other form (as part of another document or as a stand-alone
document), but the contents will be treated as an "IETF Contribution"
under the guidelines of BCP 78.
Send a copy of the template or a pointer to
the containing document (with specific reference to the section with
the template) to the mailing list
media-types@iana.org,
requesting review.
This may be combined with a request to review the media type registration.
Allow a reasonable time for discussion and comments.
Respond to review comments and make revisions to the proposed registration
as needed to bring it into line with the guidelines given in this document.
Submit the (possibly updated) registration template (or pointer to the document
containing it) to IANA at iana@iana.org.
Upon receipt of a structured syntax suffix registration request,
IANA checks the submission for completeness; if
sections are missing or citations are not correct, IANA rejects the
registration request.
IANA checks the current registry for an entry
with the same name; if such a registry exists, IANA rejects the
registration request.
IANA requests Expert Review of the
registration request against the corresponding guidelines.
The Designated Expert may request additional review
or discussion, as necessary.
If Expert Review recommends registration, IANA adds the registration to the
appropriate registry.
The initial registry content specification
provides examples of
structured syntax suffix registrations.
Registrations may be updated in each registry by the same mechanism
as required for an initial registration. In cases where the original
definition of the scheme is contained in an IESG-approved document,
update of the specification also requires IESG approval.
This template describes the fields that must be supplied in a structured syntax
suffix registration request:
Full name of the well-defined structured syntax.
Suffix used to indicate conformance to the syntax.
Include full citations for all specifications necessary to understand
the structured syntax.
General guidance regarding encoding considerations for any type employing
this syntax should be given here. The same requirements for media type
encoding considerations given in apply here.
Any issues regarding the interoperable use of types employing this
structured syntax should be given here.
Examples would include the existence of incompatible versions of the syntax,
issues combining certain charsets with the syntax, or incompatibilities with
other types or protocols.
Generic processing of fragment identifiers for any type employing this
syntax should be described here.
Security considerations shared by media types employing this structured
syntax must be specified here. The same requirements for media type
security considerations given in apply here,
with the exception that the option of not assessing the security considerations
is not available for suffix registrations.
Person (including contact information) to contact for further information.
Person (including contact information)
authorized to change this suffix registration.
Security requirements for both media type and media type suffix registrations
are discussed in .
The purpose of this document is to define IANA registries for media types and
structured syntax suffixes as well as the procedures for managing these
registries. Additionally, this document requires IANA to maintain a list of
IESG-recognized standards bodies who are allowed to register types in the
standards tree.
The existing media type registry has been extended to include a section
for provisional registrations. Only standards tree registrations are allowed
in the standards tree and only at the request of a standards body on the
IESG-recognized standards body list. See
for additional information on provisional registrations.
IANA is also requested to add the following note at the
top of the provisional registry:
This registry, unlike some other provisional IANA
registries, is only for temporary use. Entries in this
registry are either finalized and moved to the main media
types registry, or are abandoned and deleted. Entries in
this registry are suitable for use for use for development and test purposes
only.
The structured syntax name suffix registry is to be created as follows:
The name is the "Structured Syntax Suffix" registry.
The registration process is specified in .
The information required for a registry entry as well as the entry format
are specified in .
The initial content of the registry is specified in
.
Entries in both the media type and structured suffix registries will be
annotated by IANA with both the original registration date as well as the
date of the most recent update to the entry. Registrations made prior to the
implementations of this specification can be marked as "registered under
RFC 4288 or earlier".
Since registration entries can be updated multiple times,
IANA is also requested to maintain the history of changes to
each registration in such a way that the state of the
registration at any given time can be determined
Finally, this document calls for the creation of a new email address,
media-types@iana.org, for the media type review list, which replaces the
ietf-types@iana.org address specified in RFC 4288. ietf-types@iana.org should
be retained as an alias.
The current authors would like to acknowledge their debt to the late Dr. Jon
Postel, whose general model of IANA registration procedures and specific
contributions shaped the predecessors of this document . We hope that the current version is one with which
he would have agreed but, as it is impossible to verify that agreement, we have
regretfully removed his name as a co-author.
Randy Bush, Francis Dupont, Bjoern Hoehrmann, Barry Leiba, Murray Kucherawy, Alexey Melnikov,
S. Moonesamy, Mark Nottingham, Tom Petch, Peter Saint-Andre, and Jeni Tennison
provided many helpful review comments and suggestions.
Internationalized Email Headers
Update to MIME regarding Charset Parameter Handling in Textual Media TypesIsode LimitedgreenbytesAdditional Media Type Structured Syntax SuffixesAT&T LaboratoriesMac OS: File Type and Creator Codes, and File FormatsApple Computer, Inc.Deprecating the X- Prefix and Similar Constructs in Application ProtocolsCiscoBrandenburg InternetWorking
A number of media types with unfaceted subtype names, registered prior to 1996,
would, if registered under the guidelines in this document, be given a faceted
name and placed into either the vendor or personal
trees. Reregistration of those types to reflect the appropriate trees is
encouraged but not required. Ownership and change control principles
outlined in this document apply to those types as if they had been registered
in the trees described above.
From time to time there may also be cases where a media type with an unfaceted
subtype name has been widely deployed without being registered. (Note that this
includes subtype names beginning with the "x-" prefix.) If possible such
media type SHOULD be reregistered with a proper faceted subtype name. However,
if this is not possible the type can, subject to approval by both the media
types reviewer and the IESG, be registered in the proper tree with its unfaceted name.
Suffixes to indicate the use of a particular structured syntax are now fully
specified and a suffix registration process has been defined.
Registration of widely deployed unregistered unfaceted type names in the vendor
or personal trees is now allowed, subject to approval by the media types
reviewer and the IESG.
The standards tree registration process has been revised to include Expert
Review and generalized to address cases like media types in non-IETF stream
documents.
A field for fragment identifiers has been added to the registration template
and brief directions for specifying fragment identifiers have been added.
The specification requirements for personal tree registrations have been changed
to be the same as those for the vendor tree. The text has been changed to encourage
(but not require) specification availability.
The definition of additional trees has been clarified to state that an IETF
Standards Action is required.
Widely deployed types with "x-" names can now be registered as an exception in
the vendor tree.
The requirements on changes to registrations have been loosened so
minor changes are easier to make.
The registration process has been completely restructured so that with the exception
of IETF-generated types in the standards tree, all requests are processed by IANA and
not the IESG.
A provisional registration process has been added for early assignment of types
in the standards tree.
Many editorial changes have been made throughout the document to make the
requirements and processes it describes clearer and easier to follow.
The ability to specify a list of deprecated aliases for a media type has been added.
Types with names beginning with "x-" are no longer considered to be members of
the unregistered "x." tree. As with any unfaceted type, special procedures have
been added to allow registration of such types in an appropriate tree.
Changes to a type registered by a third party may now be made by the designated
change controller even if that isn't the vendor or organization that created the
type. However, the vendor or organization may elect to assert ownership and
change controller over the type at any time.
Limited use media types are now asked to note whether or not the supplied
list of applications employing the media type is exhaustive.
The ABNF for media type names has been further restricted to require that
names begin with an alphanumeric character.
Mailing list review is no longer required prior to registration of media types.
Additionally, the address associated with the media type review mailing list
has been changed to media-types@iana.org.
The rules for text/* media types have been updated to reflect the changes
specified in .